2.1. Cell lines and media
Chinese hamster ovary cells for suspension culture (CHO-S) were
purchased from Gibco, USA. CHO 1-15 cells (CRL-9606) were purchased from
ATCC, USA. Ham’s F-12 (Wako Pure Chemical Corporation, Japan) with 10%
FBS (Thermo Fisher Scientific, USA) and CHO-S-SFM II (Thermo Fisher
Scientific, USA) were used for culture of CHO-S and CHO 1-15 cells,
respectively. All media were supplemented with penicillin/streptomycin
solution (Nacalai Tesque, Japan). Cells were maintained in
CO2 incubator (Panasonic, Japan), at 37 °C with air
containing 5% CO2. Cell number was measured by Cell
Counter TC20 (Bio-Rad, USA) after staining cells with 0.5% trypan blue
solution (Nacalai Tesque, Japan).